Previous research suggests that the Hills and the Tsai-Wu failure criteria are each appropriate for predicting yield failure of human and bovine cortical bone for a limited set of stress combinations. These stress combinations were obtained by subjecting bone to tension or compression loads simultaneously with torsional loads. This set resulted in a failure locus in the fourth quadrant of the principal stress plane. It was this locus which was found to compare favorably with the Hills and Tsai-Wu criteria. The objective of this proposed research is to conduct additional tests on human and bovine bone so that the failure locus in additional quadrants is obtained. These data are necessary if failure of bone is to predicted for all possible physiological conditions. We propose to obtain the data for failure in additional quadrants by testing human and bovine bone specimens a) with combined internal pressure and torque (or axial load) and b) when subjected to double punch (shear). The failure locii will be compared to appropriate failure criteria. The test equipment and methods will be developed using young bovine bone. When the methods have been perfected tests of older bovine and of human bone will be conducted.